Perhaps one of the oldest industrial chemical processes is the production of ethanol from starchy agricultural products using natural enzymes and yeast. This process has been utilized by brewers and distillers for centuries and is currently of special commercial interest in the well-known industrial production of fuel grade alcohol from grain.
It is well known that brewers of beer preferably use malted barley. One desireable difference between barley and other common cereals is that the husk adheres to the kernel after threshing. This feature makes the process of malting and subsequent extraction of the wort much easier than with wheat or other grains.
In the beer-making process, great care is taken to make sure that crushing occurs over the whole length of the kernel. This preserves the husk almost intact to aid in filtration. A careful balance between extraction efficiency and filtration efficiency must be met.
Ancient experience teaches that if the husks of the malted barley are crushed too finely, leaching of bitter materials from the husks imparts undesirable flavor and shortened shelf life to the beer. On the other hand, beer produced entirely from dehusked malt has a very unsatisfactory flavor. Accordingly, the husks of the malted barley are a necessary part of the brewers' art.
Prior to fermentation, the brewer separates the sweet wort from the spent grains utilizing the coarse husks as a filter material. This filtering should take place rapidly with substantially all sugars washed out of the spent grains.
The very process steps necessary to produce fine beers, result in spent grain having unacceptable organoleptic characteristics. The necessity of leaving the husk of the malted barley intact results in the spent grains being course and rough. The required chemical changes during malting which gives the beer satisfactory flavor, leaves the husk bitter and organoleptically unacceptable for human food use.
A further requirement of good beer-making practice, which has detrimental effects on spent grains as a human food, is a result of the changes made in the proteins in the mash. The malted barley also contains protein-degrading enzymes, notably protease, which converts proteins into peptides and amino acids during mash digestion. These nitrogeneous peptides and amino acids are soluble and are filtered away from the spent grains to be used in the wort. This generally results in lower protein levels in the spent grains. These nitrogenous materials are later precipitated from the fermented beer and added back to the spent grains, which increases bitterness because of exposure to the fermentation process.
Currently, corn is the most popular grain used to commercially manufacture fuel alcohol. The process typically involves a two-stage enzymatic conversion of starch to sugar, followed by fermentation and then distillation to recover alcohol and carbon dioxide. Manufacturers typically dry the grain residue and sell the dried product, commonly called "Distillers' Dried Grains," as an animal feed or as a component of animal feed products. The soluble portion of the residue is often dried separately.
At the present time, wheat or other grains are not an economical choice as a fermentation substrate unless the spent grain can be sold for a higher price as human food rather than animal feed. Wheat residues are generally higher in protein, lysine, and threonine than corn residues. The process for manufacturing alcohol from wheat is very similar to that of corn.
Utilization of alcohol production residues have received little application beyond use in animal feeds. A major problem with distillers' grain residue is that it possesses a distinct odor and taste which negatively affects acceptability even for use in animal feed. Many attempts have been made throughout the years to find acceptable human food grade applications for Distillers' Dried Grains and Brewers Spent Grains, but without success. For a thorough discussion of the use of Distillers' Dried and Brewers' Spent Grains in human food, see U.S. Pat. No. 4,828,846 to Rasco, et. al. which is hereby incorporated by reference.
Rasco, et. al. teaches that the unpleasant taste and odor of Distillers' Dried Grains may be masked or reduced by the careful adjustment of pH by suitable acids and bases during starch conversion and before drying. The spent grains so treated may be used in human food products. Although an improvement over the dried grains of the typical alcohol production process, these products have proven only marginally successful. The grain products so produced still have an unacceptable taste and must be used at low flour substitution levels.